Field of the Invention
The invention, according to the various embodiments described herein, relates to a method and a device for detecting structures, such as edges and material transitions on and/or in an object under investigation, comprising an antenna array with synthetic focusing.
Discussion of the Background
Active imaging-antenna arrangements in the millimeter and microwave range have gained increasing importance through the versatility of their potential applications in the fields of medicine and industry. Such antenna arrangements comprise a plurality of individual transmission and reception antennas, whereas each antenna transmits a signal in succession, and the signal reflected from the object is received by all of the reception antennas. This is implemented either at a single frequency or stepwise at different frequencies. In this context, both the magnitude and also the phase of the received signal are registered. Using a digital beamforming algorithm (digital beamforming), it is possible to calculate back from the registered signals to the corresponding object points which have reflected the received signals and to prepare a three-dimensional image of the entire body in this manner.
Such an antenna arrangement is described, for example, in DE 10 2009 040 450 A1. The antenna arrangement described here is for the detection of concealed dielectric objects. Accordingly, the transmitted microwave signal is almost totally reflected from the human body because of its high water content and associated high permittivity. By contrast, a dielectric object arranged on the body reflects only a part of the signal from the front side of the object because of its relatively lower permittivity; another part of the signal is reflected from the rear side of the object at the limiting surface with the human body. From the interference of the two partially reflected microwave signals, it is possible to infer the presence of a dielectric region and accordingly to distinguish and visualize the dielectric object by contrast with the human body.
In this context, it is often difficult to distinguish the edge of the object from structures which arise as a result of the illumination boundary of the object. Furthermore, it is also desirable to be able to investigate the internal structure of a dielectric body, for example, with regard to influences or layers made from another material. This is particularly relevant for material investigation.